Fixed issue #2227

Added two new monitoring events:
 - ZMQ_EVENT_HANDSHAKE_SUCCEED is raised once the encryption handshake succeed
 - ZMQ_EVENT_HANDSHAKE_FAILED is raised when it failed
Both events are raised on server and client side.

src/stream_engine.hpp

@@ -65,7 +65,8 @@ namespace zmq
         enum error_reason_t {
             protocol_error,
             connection_error,
-            timeout_error
+            timeout_error,
+            encryption_error
         };
 
         stream_engine_t (fd_t fd_, const options_t &options_,